Null object pattern: Difference between revisions

Revision as of 13:58, 21 October 2020

Revision as of 08:00, 19 January 2021

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In most object-oriented languages, such as [[Java (programming language)|Java]] or [[C Sharp (programming language)|C#]], [[Reference (computer science)|references]] may be [[Null pointer|null]]. These references need to be checked to ensure they are not null before invoking any [[Method (computer science)|methods]], because methods typically cannot be invoked on null references.

The [[Objective-C|Objective-C language]] takes another approach to this problem and does nothing when sending a message to <code>nil</code>; if a return value is expected, <code>nil</code> (for objects), 0 (for numeric values), <code>NO</code> (for <code>BOOL</code> values), or a struct (for struct types) with all its members initialised to <code>null</code>/0/<code>NO</code>/zero-initialised struct is returned.<ref>{{Cite web|url = https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithObjects/WorkingwithObjects.html#//apple_ref/doc/uid/TP40011210-CH4-SW22|title = Working with Objects (Working with nil)|date = 2012-12-13|accessdateaccess-date = 2014-05-19|website = iOS Developer Library|publisher = Apple, Inc.}}</ref>

== Description ==

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| first = Martin

| last = Fowler

| authorlinkauthor-link = Martin Fowler (software engineer)

| year = 1999

| title = Refactoring. Improving the Design of Existing Code

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| first = Joshua

| last = Kerievsky

| authorlinkauthor-link = Joshua Kerievsky

| year = 2004

| title = Refactoring To Patterns

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| first = Robert

| last = Martin

| authorlinkauthor-link = Robert Cecil Martin

| year = 2002

| title = Agile Software Development: Principles, Patterns and Practices